There is an associated manual for each product made available by Server Elements. I am sure that taking a look at the appropriate manual for your version of NASLite would have answered both of your questions.
The floppy disk versions of NASLite have no concept of USB, so even though it may be possible to boot from a USB floppy - BIOS permitting, NASLite can't save the necessary configuration since it can't see the boot floppy.
Since power went out wjile your machine was active and drives mounted, NASLite needs to check and if necessary fix the filesystems. That takes a bit of time. If you take a look at the HD LED, you'll notice that it's on while NASLite is checking the drive. The check may take some time, so boot the machine and walk away for a while. It will finish eventually.
Anyway, enjoy NASLite